Preliminary studies have shown a decline in the ratio of the renal clearance of procainamide to that of creatinine as people age. The proposed study is to explore the relationship of age to the renal clearance of some organic bases, determine the degree of accumulation of these bases in the elderly and determine the pharmacologic consequences of this accumulation. Measurements will be made of the glomerular filtration rate (GFR) and renal clearance of cimetidine, trimethoprim, and glycinexylidide which is a final metabolite of lidocaine. This metabolite will also be measured in the elderly with CNS toxicity from lidocaine therapy. This study using a variety of pharmacological methods as well as the knowledge and skills of internal medicine will help understand some of the differences between the elderly and the young in drug response and also, perhaps, some pharmacologic aspects of the aging process, itself.